Every year the microelectronics industry produces faster chips with smaller and smaller devices. The industry is constantly devising new strategies and techniques for manufacturing integrated circuit chips more efficiently and with greater production yield. There is a current push to use low-k dielectric materials as insulators for the multilevel interconnect structures. Low-k dielectric materials reduce RC delay and reduce parasitic capacitances, but low-k dielectric materials are typically weak in strength and prone to cracking, scratching, delamination, and other failure modes. At the same time, copper is currently the metal of choice for providing interconnect lines. In the past, aluminum was often used. Although copper provides better electrical properties than aluminum, copper is more difficult to process. Using conventional chemical mechanical polishing (CMP) for planarizing the work piece works fine for copper, but CMP of copper requires a higher down force on the substrate than other materials, such as aluminum. This exerts large forces on surrounding low-k dielectric materials, which may lead to damage of the low-k dielectric materials and lower yields.
To successfully introduce low-k dielectric materials in combination with copper lines, low down force planarization techniques for copper were needed. This lead to the development and use of electrochemical mechanical polishing (ECMP) tools. Such ECMP tools combine techniques from electropolishing and CMP to provide a low down force planarization technique for copper while maintaining global and local planarity for copper planarization steps.
ECMP removes conductive materials from a substrate surface by electrochemical dissolution while polishing the substrate with a reduced mechanical abrasion compared to conventional CMP processes. The metal ions dissolve into a surrounding electrolyte solution at a rate proportional to the electrical current. The metal ions from the substrate (anode) plate the electrode (cathode), fall out of the solution as a precipitate of complexes, or remain in the solution. The destination of the metal ions depends greatly upon the chemistry of the metals and the solution. Chelating agents, corrosion inhibitors, pH adjusting agents, or combinations thereof may be used in the electrolyte solution to reduce damage to the low-k dielectric material during ECMP processing.
Typically in an ECMP tool, the anode electrode makes physical and electrical contact with the wafer workpiece. Similarly, electrochemical plating (ECP) tools may use the same anode electrode or a similar electrode that makes contact with the wafer. Often an ECMP tool and an ECP tool are combined at a same station or part of a same tool assembly. The surface of the electrode needs to be clean and smooth to provide good contact with the wafer. Poor contact may induce a large IR drop or an open, which will impact process quality significantly. The anode electrode may be scratched, corroded, oxidized, burned, worn out, or combinations thereof, over time from usage. Under current operations using current electrochemical processing tools (e.g., ECP and/or ECMP), the electrode that contacts the wafer is checked visually by a person once per day. However, if the electrode becomes damaged at some point during that day, the production yield for that day may be impacted significantly. Hence, there is a need for a way to monitor the condition of the electrode in an electrochemical processing tool more frequently, but without the need for a person to come to the tool each time.